This research proposal focuses on the study of the cellular function in vascular cells of two gradient-driven transport systems: the Na/H exchange and the Na-K-Cl cotransport. Our research proposal will test the new hypothesis that the link between Na transport and calcium ions in the hypertensive process relies on two processes: (i) the functional coupling of gradient-driven and pumps for Ca and Na transport, (ii) the second messenger role of calcium ions in the regulation of Na transport. The experiments proposed are designed to gain insight firstly into their transport mechanisms in order to define how they regulate the K, Na, Cl and H gradients; secondly, to investigate their functional coupling with other Ca and Na transport systems and define how they determine the cytosolic Ca available to the contractile apparatus; thirdly, to determine how they are regulated by vasoactive substances involved in blood pressure regulation. As a long range goal, we week to define in vascular cells of genetic strains of hypertensive rats whether alterations of these transport systems exist in their structural assembly, or in the mechanism of modulation. To this end, we will investigate (1) the cellular function of the Na/H exchange system in vascular smooth muscle. To determine how this transport system regulates cellular pH and dissipates the Na gradient, we will investigate the set of H and Na gradients at which the system operates as Na/H and Na/Na exchange. We will investigate the functional coupling of the Na/H exchange with the Ca pump, Ca/Na exchange and Na pump. We will study its regulation by second messengers (Ca, cAMP and cGMP) and Ca mobilizing vasoactive peptides involved in blood pressure regulation. (2) The cellular function of the Na-K-Cl cotransport in vascular cells. To test the hypothesis that this transport system is a powerful regulator of the Na, K and Cl gradients, we propose to study the equilibrium position for outward and inward cotransport to define the set of ionic gradients at which it operates to extrude Na uphill or to accumulate Cl, Na and K. To investigate the mechanism of regulation, we will determine its mode of operation and stoichiometry. We will investigate the role of cell volume changes, cytosolic Ca, cAMP, vasoactive peptides (angiotensin, bradykinin) in the regulation of the cotransport.